At present, most digital magnetic recording systems, such as those used for hard disk drives for personal computers, do not erase previously recorded data before recording new data. This is commonly known as recording in a direct overwrite mode. However, it has been found that writing in a direct overwrite mode increases the uncertainty of the exact location where a magnetic transition has been placed corresponding to the new data. This uncertainty reduces the system's signal-to-noise ratio (SNR) which has the practical limitation of reducing the system's effective storage capacity. As the bit lengths in digital recording become shorter from their already submicrometer dimensions, the ability of existing systems to write sharp transitions at particular locations lessens due to the previously written data encountered in the direct overwrite mode. As a result, signal degradation in the form of signal amplitude reduction, output pulse shape broadening, and pulse position shifts are experienced. This continuing progress in reducing the size of bit lengths and track dimensions require even more accurate recording of sharp transitions to achieve digital data density resulting in improved performance. Therefore, erasing previously recorded magnetic information would be desirable in any digital magnetic recording system, but practical implementation of this erase operation remains elusive for many applications. For example, consider the tracks in rigid disk systems. These tracks are narrow, nearing the micrometer width, are separated by distances smaller than even the track width's micrometer dimension, and these track dimensions are rapidly shrinking with each new product iteration seeking greater data density. In these applications, erasing previously recorded data before writing with conventional magnetic recording heads might be thought of in a couple of ways. One such way is for the read/write head to erase the portion (sector) of the track to be recorded on one pass of the head, and then the next pass of the head would be used to record new digital data on the previously erased sector. An obvious drawback with this approach is that it would require a time consuming extra revolution for all write steps. This delay, presently 16 milliseconds for a 3600 rpm disk drive, is larger than any other single delay for the system and would degrade overall data transfer performance. Another approach could include providing a separate erase head physically positioned "upstream" of the conventional write head, and displaced in position as with other prior art video or audio erase heads. In analog audio or video tape recording, an erase step is used to precondition the medium by erasing the old information with a separate erase head. In these systems, the erase head is physically distinct and separated from the recording head spatially and in design. The erase head may be displaced from the record head by several centimeters; may erase multiple tracks of old information in the same pass; may have a large magnetic gap for deep penetration of the magnetic field into the medium; and may use a single DC or AC applied current to erase the medium. However, there are problems in utilizing this approach with digital magnetic recording systems including the problem of physically aligning the two heads with respect to each other and with respect to the track to be overwritten. At present data densities and track dimensions, this is at least difficult and perhaps overwhelmingly challenging with track pitches projected to be 100 nanometers or less, especially considering that the heads must be consistently aligned over time, with temperature and other mechanical deviations providing further complications. Still another approach would include fabricating a second head to perform the erase function directly over the conventional write head. This approach could be considered in thin film heads which are widely used for digital magnetic recording systems. However, there would be significant cost and complexity added to the manufacturing process due to the additional steps involved with this approach.
To solve these and other problems in the prior art, the inventor has succeeded in developing a design for a thin film head with an integrated preconditioning gap which may be constructed with only a slight modification to the present manufacturing techniques utilized to construct thin film recording heads. It is anticipated that this modified construction may be achieved with only a small processing cost and without significantly reducing the expected yield of the delicate thin film manufacturing process. In essence, the inventors' design utilizes the same layering of a first magnetic pole piece, a pancake magnetic coil, and a second magnetic pole piece magnetically coupled to the first pole piece with one set of edges being spaced to form the magnetic gap therebetween. However, the bottom or first pole piece would have an extended length so as to underlie the entirety of the pancake coil, and a third pole piece is provided which magnetically couples to the extended tail of the bottom or first pole piece to thereby encircle the back half windings of the pancake coil. The second gap or preconditioning gap is thereby formed between this additional third pole piece and the second pole piece.
In sum, using conventional thin film manufacturing techniques and present designs, a thin film magnetic recording head may be conveniently manufactured with an intricately formed preconditioning gap to provide an on-the-fly erase function. This device has applicability to both perpendicular and longitudinal recording. Due to its being manufactured in an integral, single head, the preconditioning gap is always aligned with the write gap and suffers the same environmentally induced degradation such as through temperature, stress, or the like such that it remains so. Furthermore, there is no intervening spacing between the preconditioning gap and the write head as the center pole piece forms part of the magnetic circuit for each of these two gaps. Therefore, once manufactured, the preconditioning gap is aligned, its performance may be measured and tested to verify its operating parameters, and could be expected to remain in that condition over time and through its useful life. As the center pole piece is energized by a single coil, and the center pole piece forms part of the magnetic circuit for both gaps, there is no requirement for a second magnetic coil. This reduces cost, manufacturing complexity, eliminates alignment problems, and contributes to the invention's elegantly simple design. Furthermore, there is no need for a separate "erase" signal as the write signal which energizes the coil is used.
This same concept may also be implemented in a ring head coil construction with a center pole comprising an I-pole piece having a coil wrapped therearound and two C-pole pieces surrounding the I-pole piece.